There has been a post in this section, within the past few months, from someone who forfeited a bottle of whiskey for exactly the reason you've stated, so you should regard the answer to your question to be 'Yes'.
I don't know what happened there, wrong link, I can't get the right one up. Put "connecting flights" in the search box, perhaps you can get the right one, there are a couple at the top of the list.
That's odd, Boxtops. Your link appears to be a valid one but it only goes to the AB home page. (I tried to find the link which my post related to but I was unable to locate it).
If you buy in Paris, it depends on how SA deal with incoming passenger transferrring to another internal flight. In the USA, luggage is collected at the first point of entry and it is possible to put duty free into the bags before they go onto the next flight. I suppose it's a bit risky with bottles of alcohol, I've done it with perfume.
Contact the airline and ask for their advice about transferring to internal flights.
I can confirm that you will have access to your luggage in Johannesberg to pack any duty free bought in Paris. You have to take it through customs and check in again